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defeat by Hephthalites

...in repelling an invasion by the Hephthalites. In the following decades, however (the second half of the 5th century), Hephthalite attacks continued to harass and weaken the Sāsānians.
Fīrūz (reigned 457–484) fell in battle against them; his treasures and family were captured, and the country was devastated. His brother Balāsh (484–488), unable to cope...